This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. DNA polymerase kappa (Polk) has been shown to bypass certain DNA lesions and to extend from the unrepaired mismatches that inhibit normal DNA synthesis. We have solved the structure of the apo-form of the protein, as well as the co-complex with DNA to 2.40 and 3.05 angstroms respectively. We have recently characterized a new crystal form of the Polk-DNA complex, as outlined in specimen 1 above, and we are optimistic that the new packing arrangement within the crystal will allow us to collect sub-three angstrom data with the co-complex. These data will allow us to pursue further experiments to understand how the Polk active site accommodates a variety of DNA distortions. Translational repression is a highly conserved mechanism of gene regulation in eukaryotes, especially during embryogenesis. We have solved the structure of two proteins involved in such repression -- human pumilio and drosophila smaug. CNOT6 is involved in translational repression as a subunit of the CCR4-NOT deadenylation complex. To understand the role of CNOT6 in mRNA degradation, we have obtained the crystals described in specimen 2 above. These crystals are being further optimized to obtain higher resolution data.